Young men who have sex with men (YMSM) report significantly higher rates of alcohol and substance use compared to their heterosexual peers. 1-8 Increased substance use is associated with sexual risk in this population.9-14 Research that has examined the psychosocial determinants of substance use in this population has relied on samples of men recruited from traditional gay venues (e.g., gay bars) that condone substance use.11,15-20 Moreover, venue-based recruitment strategies have been criticized for excluding YMSM who do not identify as sexual minorities (e.g., gay, bisexual) but have sex with men, and those who have a limited connection to the gay community. 21 This sampling bias may lead to inflation of substance use prevalence rates and cloud the pathways of significant psychosocial determinants of risk in this population. Further, recent literature indicates that YMSM are increasingly using technology to connect with men rather than using physical venues. 23 Geosocial networking applications (GSNA) were introduced to smartphones in 2009 and it is now estimated that up to two thirds of YMSM use GSNA in the United States. 36 GSNA provide a home- screen based format that allows YMSM to connect with other men in their local area by browsing user profiles, determining the relative distance of other users, and enabling internal private messaging. Recent studies have examined the use of GSNA for recruiting a probability sample of YMSM, given that the technology allows filtering by age. 26,37-39 Despite its potential as an innovative recruitment method very few studies have utilized GSNAs to recruit YMSM, and no known study has compared this novel sampling method with conventional venue-based recruitment. Therefore the proposed study seeks to use a cross sectional online survey approach to investigate whether there are differences in sample characteristics (i.e., substance use, psychosocial determinants of substance use, demographics, and sexual risk) and feasibility (i.e., cost and recruitment efficiency) between venue-based recruitment and GSNA recruitment of a probability sample of YMSM from the a specific area of Los Angeles. The venue-based stratified probability sampling methods in this proposal are modeled after the Healthy Young Men study,30 while the GSNA probability sampling methods proposed were previously used by Rice et al.26 In addition to the random recruitment methods used in the GSNA sampling, a user density enumeration stage is proposed, which uses geographic information systems analysis and anonymous user density data, to systematically identify geographic points for random recruitment.42 Both recruitment models will be implemented simultaneously in four stages: 1) building the study sampling frame, 2) enumeration of the sampling frame to identify locations for random recruitment, 3) creation of the monthly sampling calendar, and 4) sampling events to recruit two samples: a venue-based probability sample and a GSNA probability sample. Survey data will be used to inform potential bias in recruitment approach while feasibility data will be used to make recommendations for future substance use research with YMSM.